Not applicable.
Not applicable.
The present invention relates to pumps and in particular to compact piston pumps.
Pumps for medical applications, such as used in oxygen concentrators, generally need to be compact and quiet to operate indiscreetly in homes and hospitals. It is thus important to properly muffle the working air as wells as reduce vibration during operation of the pump.
One problem with conventional pumps is that they can create excessive noise and vibration as the piston(s) are reciprocated, especially if they are improperly balanced. One reason for this in opposed piston pumps is that the pistons may be coupled to the drive shaft by a single retainer or eccentric element between the connecting rods of the piston. Ordinarily, an eccentric element is mounted to the drive shaft and two nibs or bosses extend axially from each side of the eccentric element to mount the pistons to the drive shaft. A moment, or shaking couple, arises as the drive shaft is turn because of the axial spacing between the pistons.
Another problem with conventional pumps is sealing the crankcase and cylinder(s). Improper sealing of the cylinders to the crankcase or the valve head(s) can cause pressurized air to leak to the outside of the pump, which both reduces pumping efficiency and makes noise. Typical sealing arrangements are either prone to leakage or require costly machining operations on the valve plate. Also, many crankcases are make with open necks to allow the pistons to be slid into the crankcase easily during assembly. Typically, the openings in the neck terminate at the cylinders, which have curved exterior surfaces. This makes sealing the crankcase difficult and typically requires separate seals in addition to that sealing the end of the crankcase, thus increasing assembly complexity and creating a potential leak path between the neck seals and the end seal.
Another problem with conventional pumps is that the valve stops can create excessive noise during operation. Typically, thin flapper valves are used to control the intake and exhaust ports of the valve heads. Because of the exhaust port opens under the force of the compressed air, a valve stop is used to support the valve and prevent it from being hyper-extended beyond its elastic range. Usually the stops have undersides that ramp up from the valve plate to support the tip of the valve farther from the valve plate than the neck of the valve. The valves are usually metal and the stops can be metal or plastic, however, in either case the rapid contact between the two surfaces can generate tapping or clicking sounds that are unacceptable in medical applications. Another problem here is that the thin flat flapper valve can succumb to surface attraction between the flapper and the stop and essentially xe2x80x9cstickxe2x80x9d to the stop and thus remain open.
Yet another problem confronting the design of low-noise pumps is properly muffling the intake and/or exhaust chambers of the valve heads. This can be done by attaching a muffler element to the valve head either direction or via suitable hoses. Another technique is to run the exhaust air into the crankcase on the non-pressure side of the piston head. In this case, if the crankcase is closed and the pistons are in phase, the crankcase will usually be vented through a muffler to avoid generating pulsations in the pump. Even using the later technique, the valve heads are usually exhausted through hoses leading to the crankcase, which is vented through a muffler directly mounted to the crankcase or at the end of a hose.
Accordingly, an improved pump is needed which addresses the aforementioned problems.
In accordance with one aspect, the invention provides a piston and drive shaft assembly for a pump. The assembly has first and second pistons each having a head and a connecting rod. The connecting rods have respective first and second openings. First and second bearings are fit into the respective first and second openings of the connecting rods. First and second eccentric elements are fit into the open centers of the respective first and second bearings. The eccentric elements each have an axial through bore and extend axially to one side substantially no further than a face of the corresponding piston connecting rod such that the pistons can be mounted on the drive shaft with the connecting rods axially offset and substantially adjacent one another.
In preferred forms, the eccentric elements are disk shaped and they each have an axial dimension no more than substantially the axial dimension of the connecting rods. Preferably, the piston connecting rods are mounted to the drive shaft spaced apart no more than {fraction (1/16)}xe2x80x3. The eccentric elements are preferably press-fit into centers of inner races of the bearings. In the event that the pistons have different masses, for example when one piston has a larger piston head, cup retainer elements can have differing masses weighted to bring the moments effected on the drive shaft by the pistons near equilibrium. The heavier retainer is used with the lighter piston connecting rod and pan to equalize the total mass of each piston assembly. One way to accomplish this is to make the retainers of different sizes and/or materials. For example, one retainer can be zinc and the other magnesium or aluminum.
In another aspect the invention provides a cylinder seal assembly. The cylinder has a circular end defining an oblique circumferential surface tapering radially. The oblique surface has a circumferential groove sized to receive the seal, preferably a resilient o-ring. The assembly preferably attaches to a valve plate having a circular recess defining a circular surface at an oblique angle corresponding to the oblique surface of the cylinder against which the seal can seat.
In yet another aspect the invention provides an assembly for enclosing an open-necked crankcase, having an open end and a neck opening extending from the open end to a cylinder extending essentially perpendicularly to the neck. The assembly includes a resilient seal backed by a rigid backing plate. The seal contacts the open end of the crankcase and has a plug section extending into the neck opening and having a contoured sealing surface abutting the cylinder. The backing plate covers the open end of the crankcase and has a plug support contacting the plug section of the seal.
In preferred forms, the seal is open at its center and extends into the crankcase to seal off the open face of the crankcase. The seal is preferably resilient, but the depth of the seal gives it some rigidity. The seals has a plug section for each opening in the neck of the crankcase. The sealing surface of the plug section(s) are concave and the plug sections are each formed with a ledge facing opposite the sealing surface which is engaged by the plug support of the backing plate. In opposed two cylinder pumps, the seal and cover have two plug sections and two plug supports spaced apart 180 degrees. The seal can also include one or more channel plug portions which align with open ended channels formed in the crankcase and the backing plate would then have radially extending tabs for backing the channel plugs. The channel plugs not only close of the channels but also aid in properly centering and orienting the seal on the face of the crankcase.
In still another aspect the invention provides a valve stop for retaining and supporting a flapper valve. The valve stop includes a body for attachment to a valve plate or to be cast as part of the valve head, an arm of decreased dimension extending from the body and a hand at the end of the arm having an underside spaced from an underside of the body and having at least two spaced apart lobes. Preferably, the valve stop has two arms each with a three lobed hand the undersides of which taper away from their respective arms. The lobes are preferably spaced apart equiangularly. The body further defines an alignment tab extending between the arms.
A further aspect of the invention provides a pump with one or more transfer tubes for passing air from one or more valve heads to the crankcase or to another valve head. In particular, the pump is a 180 degree opposed piston pump with both pistons located to one side of the motor. The pump has a crankcase defining a chamber, a cylinder and a transfer opening. A valve plate is mounted to the cylinder. The valve plate has intake and exhaust ports in communication with the working air inside of the cylinder. The intake and exhaust ports are opened and closed by valves mounted to the valve plate. A valve head is mounted to the valve plate to separate the intake port from the exhaust port and define respective intake and exhaust chambers. The valve plate further has a transfer port located in one of the chambers. The transfer tube is connected between the valve plate transfer port to the crankcase transfer opening.
Multi-cylinder pumps can have multiple transfer tubes connected to one or more transfer ports in the valve plate for each cylinder. For example, the transfer tubes can couple the intake or exhaust chambers to the inside of the crankcase, or they can couple multiple exhaust chambers together and/or multiple intake chambers together or the exhaust chamber of one valve head to the intake chamber of another valve head.
The crankcase can form integral passageways leading from one or more transfer openings at which the transfer tube(s) are connected. The passageway can open into the crankcase chamber in phase or run between transfer openings to join one or more chambers of one valve head with the chamber(s) of another valve head.
In preferred forms, the passageways and transfer tubes have opposing flat side walls. The transfer tube can be separate from the valve plate and the crankcase or formed as a unitary part of either the crankcase or the valve plate or both. Resilient seals can be disposed between the ends of the transfer tubes and a transfer opening in the crankcase and/or the intake and exhaust transfer ports in the valve plates as needed. The transfer tube(s) can be made of a resilient material and have stepped ends sized to fit into transfer ports. Preferably, the transfer tube(s) are clamped between the valve plate(s) and the crank case.
The invention thus provides a compact pump with considerable noise reduction and improved efficiency. These and other advantages of the invention will be apparent from the detailed description and drawings. What follows is a description of the preferred embodiments of the present invention. To assess the full scope of the invention the claims should be looked to as the preferred embodiments are not intended as the only embodiments within the scope of the invention.